Tolerance on A321 ?

[Hoangminh90]

When i did a instrument checked and i know that the tolerance between 2 NDs is 4 degree . But we also checked on the stanby compass . Sometimes it exceed 4 and i could not find the tolerance for stby compass ( on FCOM )
Another question when we are under radar control during approach , what is the maximum speed we can exceed ( select on pfd ) folowed by atc speed clearance ?

[mikedreamer787]

Did you read the compass correction card?

[Hoangminh90]

It's only 1 degree difference

[peekay4]

The magnetic compass tolerance limit is defined by regulation.

FAA specifies +/- 10 degrees in level flight:

§25.1327 Magnetic direction indicator.

(a) Each magnetic direction indicator must be installed so that its accuracy is not excessively affected by the airplane's vibration or magnetic fields.

(b) The compensated installation may not have a deviation, in level flight, greater than 10 degrees on any heading.

[mikedreamer787]

Ref (b) peekay in the last 15 years I've only ever found a maximum of 3 degrees compass correction. I should go along for a compass swing and see how its done these days. Might be more high tech.

By the way what date was 25.1327 gazetted?

[IFixPlanes]

The maintenance manual state:
make sure that
- the difference between the magnetic heading values on the standby compass and the ND is not more than + or - 8°

[FlightDetent]

Originally Posted by Hoangminh90

When i did a instrument checked and i know that the tolerance between 2 NDs is 4 degree . But we also checked on the stanby compass . Sometimes it exceed 4 and i could not find the tolerance for stby compass ( on FCOM )

There is no Airbus operational procedure to check the standby compass, therefore you will not find any limits in FCOM.
As long as your airline requires you to make the crosscheck, they need to give you some limiting values themselves, as well as proposed course of action on what to do next.

Originally Posted by Hoangminh90

When we are under radar control during approach , what is the maximum speed we can exceed ( select on pfd ) folowed by atc speed clearance ?

As accurately as possible. No intentional difference between actual speed and instructed speed should be made.

This is, of course quite impractical in a limited number of certain situations. I like the guidance provided by CAA Netherlands for Amsterodam Schipol Airport: Speeds above 220 kt (are to be) accurate within 10 kt, speeds below 220 kt within 5 kt.

My personal procedure is to fly as accurately as I can, if different speed is desired, always ask - pilot and ATC workload permitting.

NOTE: you ask about PFD selected speed, I believe the actual indicated speed is the point of discussion.